The present invention broadly relates to an improved liquid coating composition and more particularly to an improved waterborne pigmented acrylic hydrosol coating composition and process which overcomes many of the problems and disadvantages associated with acrylic hydrosol compositions of the types heretofore known.
A variety of waterborne liquid coating compositions incorporating acrylic copolymers including acrylic hydrosols have heretofore been used or proposed for use. Typical of such coating formulations are those described in U.S. Pat. Nos. 3,705,124; 3,943,187; and 4,477,609; and British Pat. Nos. 1,114,133 and 1,109,656. A method for preparing acrylic hydrosols suitable for forming waterborne acrylic coating compositions is described in a publication entitled "Acrylic Hydrosols-A New Concept in Aqueous Coating Systems" by Beardsley et al, published in Volume 40, No. 521, June, 1968 of the Journal of Paint Technology, pages 263-270. A continuing problem associated with such waterborne liquid acrylic coating compositions of the types heretofore known has been the inclusion of surfactant-type dispersing and/or emulsifying agents to provide for a stable coating composition in which the surfactant upon drying of the coating composition is incorporated into the resultant polymeric film. The presence of such surfactants in the liquid coating composition can result in flash rusting of corrosion susceptible substrates upon application and the presence of such surfactants in the resultant film renders them moisture sensitive and therefore susceptible to deterioration upon exposure to high moisture-containing environments such as, for example, those encountered by exterior coatings for automotive applications.
The present invention overcomes such disadvantages in providing a waterborne pigmented acrylic hydrosol coating composition and method of preparing such composition which is substantially devoid of any surfactant-type dispersants and/or emulsifying agents providing a liquid coating composition having excellent physical properties, which is resistant to rust formation when applied to corrosion susceptible substrates, which can be directly applied to ferrous substrates without causing flash rusting upon application and can also be applied over rusted surfaces with good adhesion, which produces polymeric films that are resistant to deterioration upon exposure to high moisture environments, which are compatible with and can be directly applied over painted surfaces without lifting of the underlying coating and which in turn is receptive to a further topcoating as may be desired or required in some instances, and which possesses excellent filling and sealing characteristics when applied to previously painted surfaces. The coating composition of the present invention is further characterized by its versatility enabling pigmentation thereof with any one or combinations of conventionally employed pigmenting agents of the types used in waterborne coating systems and which can be formulated for air-dry as well as moderate or high temperature bake systems.